Micro viscometer

ABSTRACT

Disclosed is a micro viscometer comprising a substrate having a first chamber and a second chamber that are positioned at intervals; a thin film disposed on the substrate to cover the first chamber and the second chamber; an actuating part that disposed on the thin film corresponding to the first chamber; and a sensing part that disposed on the thin film corresponding to the second chamber, wherein at least one main trench is formed in between the first chamber and the second chamber.

TECHNICAL FIELD

This present application relates generally to a Micro Viscometer, adevice for measuring the viscosity of fluids.

BACKGROUND ART

Generally, viscosity is a coefficient that expresses the physicalproperty of the fluid viscosity volume, and various types of viscometersare developed and used to measure this type of viscosity.

A viscometer called the Greenspan viscometer (Refer to M. Greenspan andF. N. Wimenitz, “An Acoustic Viscometer for Gases-I,” NBS Report 2658(1953)), which was invented in 1953 by Greenspan and Wimenitz to measurethe viscosity of gas with a design that comprises of two HelmholtzResonators that are attached and face each other, exists, however, thisviscometer relatively takes up much space and the performance shows a38% error margin that was considered not to be suitable structure.

In 1996, K. A. Gillis came up with a more precise viscometer, comparedto the Greenspan viscometer, by going through an experimental error andcorrection process to reduce the errors within the range of ±0.5% andderive more accurate gas viscosity measurements. (Refer to R. A. Aziz,A. R. Janzen, and M. R. Moldover, Phys. Rev. Lett. 74, 1586 (1995))

However, issues for this method existed, where the valid frequencysection for this method was limited only to the low frequency domain.For example, the viscometer designed by K. A. Gillis could only beapplied to low frequency under 200 Hz. The reason for this phenomenonwas because the Helmholtz Resonator was applied assuming that theproduct of the wave number of the sound wave and the characteristiclength was greatly smaller than 1. Furthermore, due to the fact that nomeasurements were made for liquids, the measurements were restricted togas and the size was large that required a mass amount of fluid.

Also, U.S. Pat. No. 6,141,625 discloses a viscosity module with acrystal resonant sensor, where this module relates to a mobileviscometer that can measure the viscosity of the fluid even with a smallquantity of reagent. This viscometer utilizes a disk type thin crystalfilm for the viscosity sensor.

To obtain this type of crystal resonant frequency, the sensor operatesin thickness shear mode by positioning electrodes on the top and bottomportion of the thin film and passing a signal. If a certain liquidexists on the top surface of the crystal, then power loss occurs thatcause damping in the crystal resonant frequency. Eventually, theviscosity of the liquid can be measured by checking the value ofdamping.

However, accurate measurements are only obtainable when a viscositymodule with a crystal resonant sensor is placed horizontally, liquid isequally distributed and a large amount of liquid. In other words, theviscosity module with a crystal resonant sensor needs several ml ofliquid with assuming that the volume of a single water drop is 0.04 mland an issue exists where it is impossible to take measurements with thevolume of a single water drop. Furthermore, this type of viscometer hasdemerits that it is impossible to make measurements of gas, since itutilizes the gravity applied on liquids.

On the other hand, many forms exist for viscometers that use thecapillary tube, however, most viscometers utilize the differential headcaused from gravity as it is disclosed in U.S. Pat. Nos. 6,322,624,6,402,703, 6,428,488, 6,571,608, 6,624,435, 6,732,573, and 5,257,529,etc. Due to the reason that the viscometer uses the differential head,measurements are limited to liquids, furthermore, issues in the amountof liquids needs exist even if capillary tubes, where the volume ofliquids necessary is more than a couple dozen to hundreds of ml that isregarded to be a large amount.

SUMMARY

A first embodiment of the present invention regarding a micro viscometercomprises a substrate having a first chamber and a second chamber thatare positioned at intervals; a thin film disposed on the substrate tocover the first chamber and the second chamber; an actuating part thatdisposed on the thin film corresponding to the first chamber; and asensing part that disposed on the thin film corresponding to the secondchamber, wherein at least one main trench is formed in between the firstchamber and the second chamber.

The main trench penetrates through the thin film and forms onto thesubstrate and the thin film up to more than 1/10 the thickness of thesubstrate.

The actuating part and the sensing part each may include a firstelectrode disposed on the thin film, piezoelectric layer disposed on thefirst electrode and a second electrode that has one side part isseparated with the first electrode and connected to the thin film, andother side part is fixed onto the piezoelectric layer.

The first electrode and second electrode may be electrically independenteach other.

An auxiliary trench may be formed onto the thin film in between thefirst electrode and the second electrode.

The thin film may include a silicon wafer and an insulator deposited ona top and a bottom surface of the silicon wafer.

A resistance value of the first thin film or the second thin film may behigher than the resistance value of the substrate.

A second embodiment of the present invention regarding a microviscometer comprises a body including an inlet where a fluid flows in,an outlet where the fluid flows out, a first chamber and a secondchamber that is connected to the inlet and the outlet, respectively, asubstrate and a cover that partition multiple micro channels thatconnect the first chamber and the second chamber; a first thin film thatvibrates with the fluid within the first chamber and locates on the sideof the first chamber; a second thin film that vibrates with the fluidwithin the second chamber and locates on the side of the second chamber;an actuating part that applies vibration onto the fluid within the firstchamber by conducting vibration through the first thin film; and asensing part that senses vibration or pressure onto the fluid thattransfers through the micro channels to the second thin film throughvibration of the first thin film, wherein the actuating part and thesensing part is electrically independent each other.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in accordance with the first embodimentof the present invention illustrating a micro viscometer.

FIG. 2 is an end view of the first embodiment of the present inventionillustrating a micro viscometer.

FIG. 3 is a graph used to explain the method of measuring the viscosityusing resonant frequency from a micro viscometer, according to oneembodiment of the present invention.

FIG. 4 is a graph used to explain the method of measuring the viscosityof the fluid using resonant frequency from a micro viscometer, accordingto one embodiment of the present invention.

FIG. 5 is a graph comparing the difference of results between thecalculation method of the Helmholtz resonator when ka<<1 and thecalculation method according to one embodiment of the present inventiondisregarding the value of ka.

FIG. 6 is a cross-sectional view of the second embodiment of the presentinvention illustrating a micro viscometer.

FIG. 7 is a graph of the absolute difference of acoustic pressureaccording to the number of micro channels when the viscosity of thefluid changes, based on the first embodiment and second embodiment ofthe present invention.

FIG. 8 is a graph of the variation rate of acoustic pressure accordingto the number of micro channels in identical conditions with FIG. 7.

FIG. 9 is a diagrammatic view of the chamber structure of a microviscometer according to one embodiment of the present invention.

FIGS. 10 a-10 b are diagrammatic views of the first resonant frequencyand second resonant frequency that are transferred within the chamber ofa micro viscometer, respectively.

FIG. 11 is the electric circuit of a micro viscometer according to oneembodiment of the present invention.

FIG. 12 is the trench structure of a micro viscometer according to oneembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view in accordance with the first embodimentof the present invention illustrating a micro viscometer and FIG. 2 isan end view of the first embodiment of the present inventionillustrating a micro viscometer.

As illustrated, a micro viscometer 100 positions 2 Helmholtz resonatorsin parallel so that viscosity can be measured even with a small amountof fluid. The micro viscometer comprises substrate a thin film 150, anactuating part 170 and a sensing part 180, a body 110 that includes asubstrate 113 and a cover 114.

The substrate 113 and the cover 114 are bonded onto the body 110 with aninterval to provide space for an inlet 111, an outlet 112, a firstchamber 120, a second chamber 130 and a micro channel 140.

The substrate 113 can be composed of a Silicon On Insulator (SOI) thatpossess a Silicon single crystal layer on top of the silicon wafer orinsulator, and space for the first chamber 120 and the second chamber130 prepared through the Deep Reactive Ion Etching (DRIE) process isprovided one side of the substrate 113.

Anodic bonding is operated on the cover 114 and the substrate 113 sothat decay space is given to the inlet 111, the first chamber 120, thesecond chamber 130, the outlet 112 and the micro channel 140. Also, amaterial of the cover 114 may be transparent material such as a glass tovisually confirm a fluid within the cover 114.

On one side of the inlet 111 and the outlet 112 of the body 110,open-close valves 191, 192 are provided so that fluids inputted withinthe body 110 does not flow outside. To open-close the fluid movement,open-close valves 191, 192 may be omitted according to a method ofmeasuring the viscosity of the fluid.

The first chamber 120 and the second chamber 130 of the body 110 areconnected to the inlet 111 and outlet 112, respectively. It is desiredfor the first chamber 120 and the second chamber 130 to havesubstantially identical volume and height. The design is to minimize anerror that may occur from the vibration applied on the thin film 150when measuring the viscosity of the fluid.

The micro channel 140 connects the first chamber 120 with the secondchamber 130 and provides space for viscosity loss of the fluid whenmeasuring the fluid viscosity within the body.

The thin film 150 is positioned on the substrate 113 to cover the firstchamber 120 and second chamber 130. The thin film 150 separates thefirst chamber 120 and the second chamber 130 from the outside and,during operation, vibrates with the filled fluids within the firstchamber 120 and the second chamber 130. This type of thin film 150 isformed in a single film, as illustrated, however, it can have additionaltwo thin films for the first chamber 120 and the second chamber 130,correspondingly.

Furthermore, the thin film 150 is formed with Silicon Nitride (SiN)laminated onto the Silicon wafer, and comprises an insulator 153attached to the top and bottom of the silicon wafer 151 as illustrated.

It is suitable to use a Si type insulator such as Silica dioxide (SiO2)as the insulator 153.

The actuating part 170 locates on the thin film 150 that corresponds tothe first chamber 120 and conducts vibration onto the thin film 150 sothat the vibration can transfer to the fluid within the first chamber120. For the convenience of explanation, the portion of the thin film150 that corresponds to the first chamber 120 is called the first thinfilm.

The actuating part 170 comprises a first electrode 175, a piezoelectriclayer 171 arranged on the first electrode 175 and a second electrode 173that is positioned on the piezoelectric layer 171. One side of thesecond electrode 173 is separated from the first electrode 175 andconnected to the first thin film, while the other side of the secondelectrode 173 is located on the first piezoelectric layer 171.

The sensing part 180 comprises the thin film 150 that corresponds to thesecond chamber 130 and senses the vibration or the pressure of the fluidwithin the second chamber 130 that is transferred to the thin film 150.For the convenience of explanation, the portion of the thin film 150that corresponds to the second chamber 130 is called the second thinfilm.

This type of sensing part 180, similar to the actuating part 170,comprises a third electrode 185 disposed on the second thin film and asecond piezoelectric layer 181 arranged on top of the third electrode185 and a fourth electrode 183 positioned on the second piezoelectriclayer 181. Thus, one side of the fourth electrode 183 is separated fromthe third electrode 185 and connected to the second thin film, while theother side of the fourth electrode 183 is arranged on one side of thesecond piezoelectric layer 181.

Meanwhile, the actuating part 170 and the sensing part 180 for examplehave used the piezoelectric layer for piezoelectric effects, however, itis not limited to this example and polymer materials with piezoelectriccharacteristic can also be utilized.

During operation, fluid, such as air, within the body 110 outflowsthrough the outlet 112 to the outside, the inside pressure decreases andthe fluid inflows within the body 110 through the inlet 111

It is suitable to have Hydrophilic surface treatment such as hydrophiliclayer done on at least one side of the compositions within the body 110of a micro viscometer 100 where it has contact with the fluid such asthe inlet 111, outlet 112, first chamber 120, second chamber 130 andmicro channel 140. This helps the inflow of the fluid within the bodyand prevents air bubble formation within the body that may occur fromsurface tension of the fluid.

On the other hand, open-close valves 191, 192 are shut off when thefluid fills the body 110 so that it can prevent the fluid to flowoutside from the body 110 interior.

Next, by providing the voltage (V_(input)) as a Sine function similar toEquation 1 below in the frequency domain that includes resonantfrequency of the system of a pair of first electrode 175 and secondelectrode 173 of the actuating part 170, the first piezoelectric layer171 applies vibration to the first thin film.V _(input) =V ₀ Sin ωt  Equation 1

When the first thin film vibrates, a loss in sound wave occur due to theacoustic boundary layer inside the micro viscometer, or in other wordsthe inside the body 110. This type of loss can be categorized into two;one is the loss(α_(v)) of the viscosity boundary layer(δ_(v)) within themicro channel that has the fastest particle velocity and the other isthermal loss(α_(t)) that comes from the thermal boundary layer(δ_(t)) ofthe first chamber 120 and second chamber 130 that has large area tovolume ratio.

When the viscosity boundary layer or the thermal boundary layer isgreatly smaller than the radius or half the height, r_(c), of the microchannel 140 this loss of the boundary layer has the relationship withthe Q factor as shown in Equation 2.

$\begin{matrix}{\frac{1}{Q} = {{\frac{\alpha_{v}}{2\pi} + \frac{\alpha_{t}}{2\pi}} = {\frac{\delta_{v}}{r_{c}} + {\left( {\gamma - 1} \right)\frac{\delta_{t}S}{\pi\; V}}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In this equation, the r is the ratio of specific heat of the fluid, s isthe area of the chamber, v is the volume of the chamber, δ_(v) is thethickness of viscosity boundary layer of the micro channel 140 interior,δ_(t) is the thickness of thermal boundary layer of the chamber 120,130.

The sound wave conveys to the second thin film possessing this loss andthe frequency response outputted from the second thin film from theeffects of the second piezoelectric layer 181 of the sensing part 180can be measured.

When measuring the Q factor for this type of frequency response Equation2 is used to measure the viscosity of fluid as shown in Equation 3.

$\begin{matrix}{v = {\frac{\mu}{\rho} = {\frac{\omega\; r_{c}^{2}}{2}\left\{ {\frac{1}{Q} + {\left( {1 - \gamma} \right)\frac{\delta_{t}S}{\pi\; V}}} \right\}^{2}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In this equation, ν is the Kinematic Viscosity, μ is the DynamicViscosity and ρ is the density.

Alternatively, a different method can be introduced, as discussed below,using a micro viscometer 100 according to one embodiment of the presentinvention, which is the Single-Frequency Driving Method (SFDM) that usessingle frequency (or resonant frequency) to measure the viscosity.

For the method for measuring the viscosity from single frequency, amethod for measuring the change or the viscosity of the fluid utilizingthe frequency (or resonant frequency) instead of the Q factor is used toovercome onerous tasks of using sweeping on the frequency domain thatapplies the Q factor and finds the resonant frequency and directlyobtains the half power band width, and also accurately deriving the Qfactor due to the error of the resonant frequency or half powerbandwidth.

As illustrated in FIG. 3, the degree of acoustic pressure of theresonant frequency occurs as the fluid viscosity changes. By measuringthe variance the change status of the viscosity can be measured and thedesired fluid viscosity can be measured through compensation process.

Thus, fluid that serves as certain standards, for example water,measures the pressure sensed through the sensing part 180 according tothe increase of frequency of the actuating part 170, and the viscosityof the this water saves data after measuring the pressure followingfrequency by stage that increase 20%, 40%, 60%, 80%, 100%, asillustrated in FIG. 4.

Afterwards, the pressure data sensed from the sensing part 180 comparedto the frequency applied from the actuating part 170 on the fluid thatneeds measurement is obtained, and then the viscosity of the fluid thatneeds measurement is derived from the viscosity value that correspondsto the obtained data. The viscosity data that serves as a standard canbe obtained more precisely than the interval of 20% as in one of theembodiments.

Also, the frequency f_(L) and f_(H) of the pressure (0.707M) isobtained, which becomes

$\frac{1}{\sqrt{2}}$of the maximum pressure (M) when the frequency alters between before andafter the viscosity change of the fluid as illustrated in FIG. 3, thenit is substituted into Equation 4 below to derive the Q factor. Theviscosity of the fluid can be derived by using the Q factor, Equation 2and Equation 3.

$\begin{matrix}{Q = \frac{f_{o}}{f_{H} - f_{L}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

In another aspect, the Helmholtz resonator is usually applied in acouple dozen to a couple hundred Hz where the character size of thesystem is greatly shorter than the frequency wavelength, also expressedka<<1. Here, the k is the wave number and a is a radius of the microchannel 140.

For this, one embodiment of the present invention uses MEMS process sothat it holds a very small and thin type compared to general viscometersand resonant frequency increases up to hundreds of thousands to tens ofmillions Hz of the system itself.

Therefore, this present device expands and interprets the frequencydomain so that is does not operate within the domain that does notsatisfy the frequency domain of the Helmholtz resonator, which is ka<<1.For this purpose, the Total Acoustic Impedance of this inventionexpresses Equation 5, and using the equation as shown in Equation 6where the reactance is 0 the resonant frequency can be derived.Z _(ac) =Z _(mem1) +Z _(ca1)+2Z _(end) +Z _(mc) +Z _(ca2) +Z_(mem2)  Equation 5

Each value for the impedance is shown below.

$Z_{{mem}\; 1} = \frac{K_{ac}^{{mem}\; 1}}{j\;\omega}$is the acoustic impedance of the first thin film 150,

$Z_{{mem}\; 2} = \frac{K_{ac}^{{mem}\; 2}}{j\;\omega}$is the acoustic impedance of the second thin film 160,

$Z_{{ca}\; 1} = {\frac{Z_{0}}{{jtan}\;{kh}_{1}}\frac{1}{S_{1}}}$is the acoustic impedance of the first chamber 120,

$Z_{{ca}\; 2} = {\frac{Z_{0}}{j\;\tan\;{kh}_{2}}\frac{1}{S_{2}}}$is the acoustic impedance of the second chamber 120,

$Z_{mc} = {j\frac{Z_{0}\tan\;{kl}}{A}}$is the acoustic impedance of the micro channel 140,

$Z_{end} = {\frac{Z_{0}}{A}\left\{ {{R_{1}\left( {2\;{kr}_{c}} \right)} + {j\;{X_{1}\left( {2{kr}_{c}} \right)}}} \right\}}$is the acoustic impedance of the inlet 111 and outlet 112.Furthermore, K_(ac) ^(mem1) and K_(ac) ^(mem2) are the AcousticStiffness of the first thin film 150 and second thin film 160respectively, h₁ and h₂ correspondingly represents the height of thefirst chamber 120 and second chamber 130, and

${{R_{1}\left( {2{kr}_{c}} \right)} = {1 - {\frac{2{J_{1}\left( {2{kr}_{c}} \right)}}{2{kr}_{c}}\mspace{14mu}\left( {J_{1}\text{:}\mspace{11mu}{Bessel}\mspace{14mu}{function}} \right)}}},{{X_{1}\left( {2{kr}_{c}} \right)} = {\frac{2{H_{1}\left( {2{kr}_{c}} \right)}}{2{kr}_{c}}\mspace{14mu}\left( {H_{1}\text{:}\mspace{11mu}{first}\mspace{14mu}{order}\mspace{14mu}{struve}\mspace{14mu}{function}} \right)}}$are each represented from Acoustic Impedance Z_(end).

If, the size and shape of the first chamber 120 and second chamber 130are the same, Z_(ac) can be more simply expressed, furthermore to findthe resonant frequency by taking the reactance of Z_(ac) can come upwith Equation 6 as shown below.

$\begin{matrix}{{{Im}\left( Z_{ac} \right)} = {{\frac{2Z_{0}}{A}\left\{ {{\frac{2}{2{kr}_{c}}\left\lbrack {\frac{2}{\pi} - {J_{0}\left( {2{kr}_{c}} \right)} + {\left( {\frac{16}{\pi} - 5} \right)\frac{\sin\left( {2{kr}_{c}} \right)}{2{kr}_{c}}} + {\left( {12 - \frac{36}{\pi}} \right)\frac{1 - {\cos\left( {2{kr}_{c}} \right)}}{\left( {2{kr}_{c}} \right)^{2}}}} \right\rbrack} + \frac{\tan\;{kl}}{2}} \right\}} - \left\{ {{\frac{2Z_{0}}{\tan\;{kh}}\frac{1}{S}} + \frac{2K_{ac}^{mem}}{\omega}} \right\}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Therefore, frequency of the k value that satisfies Im(Z_(ac))=0corresponds to the resonant frequency. By substituting a variable x forthese values, the follow Equation 7 can be derived.k _(n) =x _(x)(n:integer)  Equation 7

Resonant frequency can be derived by using Equation 8 below.

$\begin{matrix}{f_{1} = {\frac{k_{1}c_{o}}{2\pi} = \frac{x_{1}c_{o}}{2\pi}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

FIG. 5 is a graph comparing the difference of results between the casewhere ka<<1 for the Helmholtz resonator and the method that can beapplied to one embodiment of the present invention disregarding thevalue of ka.

When the calculation method of one embodiment of the present inventionholds a small radius (a) of the micro channel 140 so that the resonantfrequency (f) of the system is low, and satisfies the conditions ofka<<1, the Helmholtz resonator calculation method is approached, while,on the other hand, when the radius (a) of the micro channel 140 becomesgreater and the resonant frequency increases, and the assumption of theHelmholtz resonator calculation method, ka<<1, does not meet theconditions, the calculation method following the embodiment of thepresent invention should be applied.

FIG. 6 is a cross-sectional view of the second embodiment of the presentinvention illustrating a micro viscometer.

A micro viscometer 500 according to the second embodiment isstructurally similar to the first embodiment of a micro viscometer withseveral differences. Therefore, identical reference numerals are usedfor identical composition factors and explanations are not repeated.

Referring to FIG. 6, the second embodiment of a micro viscometer 500comprises multiple micro channels 140 on the body 110. Each microchannel 140 may have different lengths. Or, the lengths are identical sothat an acoustic pressure with the same phase angle and amplitudetransfers from each micro channel 140 and the sensing part 180 sensesthe acoustic pressure.

FIG. 7 is a graph of the absolute difference of acoustic pressureaccording to the number of micro channels when the viscosity of thefluid changes, based on the first embodiment and second embodiment ofthe present invention. FIG. 8 is a graph of the variation rate ofacoustic pressure according to the number of micro channels in identicalconditions with FIG. 7.

As it is shown from FIG. 7 and FIG. 8, when multiple micro channels areformed within the body of a micro viscometer, the variance of theacoustic pressure decreases compared to when a single micro channel isformed within the body interior, however, the acoustic pressureincreases.

For example, when the micro channel length is 3 mm in FIG. 7, and whenthe numbers of micro channels are 1 and 7 respectively, the acousticabsolute variance correspondingly turns out to be 0.05 Pa and 0.25 Pa.However, when checking the variance of acoustic pressure in FIG. 8 wherethe numbers of micro channels are 1 and 7 respectively, the acousticpressure shows similar values of 0.75 and 0.72 correspondingly.

Thus, measurements can be more greatly made for the signal of theacoustic pressure compared to the surrounding noise when measuring theacoustic pressure at the sensing part due to the effect that a greaterdegree of acoustic pressure is transferred as the number of microchannels increase.

Meanwhile, it is desirable for the first thin film and second thin filmto have identical resonant frequencies to increase the accuracy comparedto when measuring the viscosity of the fluid in an embodiment of thepresent invention that deal with a micro viscometer.

Furthermore, in order to accurately measure the viscosity of the fluideven more, the spatial structure of the chamber that forms the bodyinterior must be designed more acoustically. For this, FIG. 9 and FIG.10 are referenced to explain this matter.

FIG. 9 is a diagrammatic view of the chamber structure of a microviscometer according to one embodiment of the present invention andFIGS. 10 a-10 b are diagrammatic views of the first resonant frequencyand second resonant frequency that are transferred within the chamber ofa micro viscometer, respectively.

Referring to FIG. 9 and FIG. 10, the viscosity of the fluid within thebody can be accurately measured by the increase in the damping effect ofthe acoustic pressure, which is transferred through the first chamber120, within the micro channel 140 when the first resonant frequency thatoccurs from the thin film 150 transfers acoustic pressure to the firstchamber 120.

Namely, in order to transfer with the greatest degree of acousticpressure transferred to the first chamber 120 through the micro channel,the first resonance (a) must occur in the height direction of the firstchamber 120. Therefore, it is necessary for the height (H) of the firstchamber 120 to at least actually form a half wavelength that responds tothe first resonant frequency and the width of the first chamber 120should be shorter than the height of the first chamber 120 or the halfwavelength that corresponds to the first resonant frequency.

If the width of the first chamber 120 is longer than the height (H) ofthe chamber or the half wavelength corresponding to the first resonantfrequency, first resonance (a) occurs in the width direction of thefirst chamber 120 so that desirable acoustic pressure is not actuallytransferred through the micro channel 140. Like this, the height (H) andwidth (W) of the first chamber 120 depend on the first resonantfrequency of the thin film 150.

Furthermore, to make manufacturing process conditions simple in buildingone embodiment of the present invention according to a micro viscometer,the height (H) of the first chamber 120 should have an equal wavelengthcorresponding to the frequency in accordance with a second resonant (b)of the thin film 150.

The width (W) of the first chamber 120 should be at least smaller thanthe half wavelength of the second resonant frequency. This is becausewhen the second resonant frequency is larger than the length of the halfwavelength, the first resonant frequency of the thin film 150 with highdegree of the acoustic pressure in the width direction of the firstchamber 120 occurs which makes it actually hard for the acousticpressure transfer in the height direction of the first chamber that isthe wavelength direction of progress.

The structure of the chamber as above is not shown. However, it canidentically used not only for the first chamber 120 of the actuatingpart but also the second chamber 130 of the sensing part.

Meanwhile, to measure the viscosity of the fluid more accurately it isnecessary to cancel the noise occurring due to the electric effectbetween the actuating part 170 and the sensing part 180 when a microviscometer operates.

FIG. 11 is the electric circuit of a micro viscometer according to oneembodiment of the present invention.

As illustrated, a micro viscometer constructs the electric circuit bydividing into the actuating part and sensing part. When applying voltagein the actuating part at this moment the current following the voltageactually should not flow into sensing part so that the viscosity of thefluid can be derived from the genuine acoustic pressure.

Due to the characteristics of the substrate 113, when the voltageapplied to the actuating part is a direct current signal the electricimpedance becomes infinite so that the current following the appliedvoltage of the actuating part does not flow into the sensing part,however, when the voltage applied on the actuating part is a alternatingcurrent the impedance becomes lower which brings the resistance of thesubstrate to decrease.

The current following the voltage, which is applied on the actuatingpart, flows into the sensing part which causes inaccurate measurementsof viscosity of fluids due to an electrical noise included in theacoustic pressure measurement of the sensing part.

Therefore, as shown in FIG. 12, in a micro viscometer according to oneembodiment of the present invention, electrical separation of theactuating part 170 from the sensing part 180 is necessary.

Physically, a thin film 150 has a trench S1 formed between the firstchamber 120 and second chamber 130 so that the actuating part 170 andsensing part 180 actually has electrical separation, and the main trench(S1) extends to a portion of the substrate 113 positioned on the thinfilm bottom. The number of main trench (S1) can be at least one.

Preferably, the main trench (S1) is formed on the substrate 113 and cutsthrough the thin film 150 and has a depth of more than ½ of thethickness of the substrate 113.

When applying voltage on the actuating part 170 or sensing part 180,noise can be measured with the measurement of the viscosity of fluidfrom acoustic pressure from the effect of the applied current in betweenthe first electrode 175 and second electrode 173 of the actuating part170 or in between the third electrode 185 and fourth electrode 183 ofthe sensing part 180.

To prevent this, the thin film should provide electrical separationbetween the first electrode 175 and second electrode 173 or between thethird electrode 185 and fourth electrode 183. In one embodiment, asupporting (or auxiliary) trench (S2) can be constructed for electricalseparation between the first electrode 175 and second electrode 173 orbetween the third electrode 185 and fourth electrode 183 of the thinfilm 150.

Like this, a micro viscometer according to one embodiment of the presentinvention, enables the measurement of viscosity not only in liquid butalso gas, and since the size of this viscometer holds its merits bybeing itself the smallest model, not only does it become used as anindependent equipment exclusively for viscosity but also allows accurateviscosity measurement of the fluid when included as a component ofanother equipment.

Furthermore, as the interest on the bio technology has risen, theapplication has become various, in measurements for such as viscosityfor various fluids within the living body, including the viscositymeasurement on blood and viscosity and variance measurement of amplifiedDNA due to Micro PCR, etc.

In addition, this present invention, regarding a micro viscometer, canmeasure the viscosity and variance with only a minimal amount of fluidby utilizing MEMS (Micro-Electro Mechanical Systems) structure so thatmeasuring hardly obtainable or high cost reagents or gas is possible.Also, due to the fact that gravity does not affect the device theviscometer can disregard the location or direction of placement.Furthermore, the viscometer quickly and efficiently measures theviscosity with a character of small size that promotes the use as anindependent device and also does not take much space as a component ofanother device.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described examples are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the meets and bounds of theclaims, or equivalences of such meets and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A micro viscometer, comprising: a substrate having a first chamber and a second chamber that are spatially separated from each other; a thin film disposed on the substrate to cover the first chamber and the second chamber; an actuating part disposed on a first portion of the thin film corresponding to the first chamber; and a sensing part disposed on a second portion of the thin film corresponding to the second chamber, wherein at least one trench is formed between the first and second portions of the thin film to thereby electrically separate the actuating part from the sensing part.
 2. The micro viscometer of claim 1, wherein the trench penetrates through the thin film and extends into the substrate by a depth of more than 1/10 of a thickness of the substrate.
 3. The micro viscometer of claim 1, wherein the actuating part and the sensing part each include a first electrode disposed on the thin film, a piezoelectric layer disposed on the first electrode, and a second electrode having one side separated from the first electrode and electrically connected to the thin film and another side fixed onto the piezoelectric layer.
 4. The micro viscometer of claim 3, wherein the first electrode and second electrodes are electrically separated from each other.
 5. The micro viscometer of claim 3, wherein an auxiliary trench is formed onto the thin film between the first electrode and the second electrode.
 6. The micro viscometer of claim 5, wherein the thin film includes a silicon wafer and an insulator disposed on top and bottom surfaces of the silicon wafer.
 7. The micro viscometer of claim 1, wherein an electrical resistance value of the thin film is higher than an electrical resistance value of the substrate.
 8. A micro viscometer, comprising: a body including: a first chamber, an inlet for introducing a fluid into the first chamber, a second chamber, an outlet for discharging a fluid from the second chamber, a cover, and a substrate secured to the cover and having a plurality of micro channels for fluid communication between the first chamber and the second chamber; a first thin film disposed on one side of the first chamber and adapted to vibrate with the fluid within the first chamber; a second thin film disposed on one side of the second chamber and adapted to vibrate with the fluid within the second chamber; an actuating part for applying vibration onto the fluid in the first chamber by conducting vibration through the first thin film; and a sensing part for sensing at least one of vibration and pressure of the fluid in the second chamber, wherein the actuating part and the sensing part is electrically separated from each other.
 9. The micro viscometer of claim 8, wherein at least one of electrical resistance values of the first thin film and the second thin film is higher than an electrical resistance value of the substrate.
 10. The micro viscometer of claim 8, wherein the first thin film and the second thin film each include a silicon wafer and an insulator disposed on top and bottom surfaces of the silicon wafer.
 11. The micro viscometer of claim 10, wherein the insulator comprises a Si type layer.
 12. The micro viscometer of claim 8, wherein the actuating part includes a first electrode disposed on the first thin film, a first piezoelectric layer disposed on the first electrode, and a second electrode having one side separated from the first electrode and electrically connected to the first thin film and another side fixed onto the first piezoelectric layer, and wherein the sensing part includes a third electrode disposed on the second thin film, a second piezoelectric layer disposed on the third electrode, and a fourth electrode having one side separated from the third electrode and electrically connected to the second thin film and another side fixed onto the second piezoelectric layer.
 13. The micro viscometer of claim 8, wherein an auxiliary trench is formed in the first thin film between the first electrode and the second electrode.
 14. The micro viscometer of claim 8, wherein an auxiliary trench is formed in the second thin film between the third electrode and the fourth electrode. 